Satellite observation of hourly dynamic characteristics of algae with Geostationary Ocean Color Imager (GOCI) data in Lake Taihu

Phytoplankton bloom in a shallow inland eutrophic lake (Taihu Lake) is characterized by significant spatial and temporal variation and a high concentration of chlorophyll-a (Cchl-a). The observation of the rapidly changing dynamic characteristics of algae is limited by the insufficient temporal resolution of satellite data. The Geostationary Ocean Color Imager (GOCI), launched by Korea, can provide high temporal resolution satellite data to observe the hourly dynamics of algae. In this study, a simple regional NIR-red two-band empirical algorithm of Cchl-a for GOCI is proposed for Taihu Lake. Study results show that the GOCI-derived Cchl-a matches the in situ measured values well. Based on this validated algorithm of Cchl-a, we obtained the hourly maps of Cchl-a from GOCI level-1b data during the period August 6 to August 9, 2013. The spatial variation of GOCI-derived Cchl-a also matches synchronous in situ measured values well, and the temporal variation of GOCI-derived Cchl-a coincides with buoy-measured Cchl-a. The northwestern area of the lake and Meiliang Bay are worst hit by phytoplankton bloom. GOCI-derived Cchl-a revealed a clear evidence of hourly spatial and temporal variations of Cchl-a in Taihu Lake. The vertical current plays an important role in the hourly scale of spatial and temporal variations in phytoplankton. The horizontal current is important to the distribution of phytoplankton over the long term, but spatially and temporally limited in the short term.